I was hoping to narrow it down a little more, but here's a list of all airports that fill this criteria:
1) Had flights from T1 in Hong Kong after 'Amazing Race host' was sighted there (2pm June 1)
2) Had flights from Singapore after reported flight from Surabaya arrived (9am June 2)
3) Cannot be flown direct from Surabaya.
BKI Kota Kinabalu
BKK Bangkok
BLR Bangalore
BNE Brisbane
BOM Mumbai
DAC Dhaka
DEL Delhi
DXB Dubai
HAN Hanoi
HKT Phuket
HND Tokyo
ICN Seoul
LHR London
MAA Chennai
MEL Melbourne
MNL Manila
NRT Tokyo
PER Perth
RUH Riyadh
SGN Ho Chi Minh City
SYD Sydney
(Colombo could still be a possibility, but there were no direct flights from Hong Kong on that day)
As a side note, Allan Wu was attending a racing event about 100 miles from Hong Kong airport on June 2. However, there's a closer airport so I'd be surprised if the HKG sighting was him.